PROJECT SUMMARY Drs. Rogovskyy (PI), Stoica (Co-Investigator), Threadgill (Co-Investigator) Lyme disease, the most prevalent tick-borne illness in North America, is caused by spirochetes of Borrelia burgdorferi sensu lato complex (Bb). The estimated incidence of Lyme disease is approximately 300,000 new cases per year (www.cdc.gov). Lyme disease is problematic because early diagnosis is easily missed due to flu-like symptoms that only appear transiently in humans during the early stage of disease. When missed and, therefore left untreated, Lyme disease becomes chronic. Unfortunately, antimicrobial treatment of chronic infection is often unrewarding. Besides skin lesions, arthritis, and carditis, neurological manifestations represent the most frequent clinical involvement for Lyme disease worldwide. In the United States, approximately 15% of patients with untreated Bb infection exhibit Lyme neuroborreliosis (LNB). Both central (CNS) and peripheral nervous systems (PNS) may be affected. Despite the significance of LNB, many aspects of LNB pathogenesis remain unknown due to the lack of suitable animal model. The long-term goal of this exploratory study is to understand pathogenic mechanisms leading to LNB. Nonhuman primates currently constitute the only available model. However, issues of cost, animal availability, handling complexity, reagents availability, non-reproducible genetic backgrounds, and ethical concerns significantly limit their use. On the other hand, despite an obvious need, more affordable and advantageous mouse models have yet to be developed. Neither meningitis nor encephalitis has been documented in mice. Therefore, the overall objective is to develop a mouse model that will be permissive to Bb entry into the nervous system (NS) and will mimic human LNB. It is possible that host genetics of mouse strains are responsible for prevention of Bb spirochetes from invading and triggering inflammation in murine NS. Thus, in order to develop the mouse LNB model, we propose to pursue the following specific aim: Determine if genetically diverse recombinant inbred mice will develop LNB upon infection with Bb neurotropic strain. The approach is innovative because it will for the first time involve extensive use of the Collaborative Cross (CC) resource to develop LNB mouse model. CC lines are a genetically diverse panel of recombinant inbred mice that have been obtained through a systemic cross of eight inbred founder mouse strains. The CC lines have been successfully applied to develop first mouse models of Ebola hemorrhagic fever and Aspergillus fumigatus. The experimental design will involve 48 mouse CC lines that wll be infected with neurotropic Bb. Neural tissues will be histologically and molecularly analyzed for the presence of inflammation and Bb spirochetes. The proposed research is significant because the new model will allow the scientific community to significantly advance the field of LNB. Specifically, the LNB model will be the basis for development of new therapeutics and diagnostic tools for LNB patients.